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254 lines
6.2 KiB
254 lines
6.2 KiB
// SPDX-License-Identifier: GPL-2.0 |
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/* |
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* CFB: Cipher FeedBack mode |
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* |
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* Copyright (c) 2018 [email protected] |
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* |
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* CFB is a stream cipher mode which is layered on to a block |
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* encryption scheme. It works very much like a one time pad where |
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* the pad is generated initially from the encrypted IV and then |
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* subsequently from the encrypted previous block of ciphertext. The |
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* pad is XOR'd into the plain text to get the final ciphertext. |
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* |
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* The scheme of CFB is best described by wikipedia: |
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* |
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* https://en.wikipedia.org/wiki/Block_cipher_mode_of_operation#CFB |
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* |
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* Note that since the pad for both encryption and decryption is |
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* generated by an encryption operation, CFB never uses the block |
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* decryption function. |
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*/ |
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#include <crypto/algapi.h> |
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#include <crypto/internal/cipher.h> |
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#include <crypto/internal/skcipher.h> |
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#include <linux/err.h> |
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#include <linux/init.h> |
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#include <linux/kernel.h> |
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#include <linux/module.h> |
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#include <linux/string.h> |
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static unsigned int crypto_cfb_bsize(struct crypto_skcipher *tfm) |
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{ |
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return crypto_cipher_blocksize(skcipher_cipher_simple(tfm)); |
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} |
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static void crypto_cfb_encrypt_one(struct crypto_skcipher *tfm, |
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const u8 *src, u8 *dst) |
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{ |
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crypto_cipher_encrypt_one(skcipher_cipher_simple(tfm), dst, src); |
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} |
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/* final encrypt and decrypt is the same */ |
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static void crypto_cfb_final(struct skcipher_walk *walk, |
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struct crypto_skcipher *tfm) |
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{ |
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const unsigned long alignmask = crypto_skcipher_alignmask(tfm); |
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u8 tmp[MAX_CIPHER_BLOCKSIZE + MAX_CIPHER_ALIGNMASK]; |
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u8 *stream = PTR_ALIGN(tmp + 0, alignmask + 1); |
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u8 *src = walk->src.virt.addr; |
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u8 *dst = walk->dst.virt.addr; |
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u8 *iv = walk->iv; |
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unsigned int nbytes = walk->nbytes; |
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crypto_cfb_encrypt_one(tfm, iv, stream); |
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crypto_xor_cpy(dst, stream, src, nbytes); |
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} |
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static int crypto_cfb_encrypt_segment(struct skcipher_walk *walk, |
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struct crypto_skcipher *tfm) |
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{ |
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const unsigned int bsize = crypto_cfb_bsize(tfm); |
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unsigned int nbytes = walk->nbytes; |
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u8 *src = walk->src.virt.addr; |
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u8 *dst = walk->dst.virt.addr; |
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u8 *iv = walk->iv; |
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do { |
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crypto_cfb_encrypt_one(tfm, iv, dst); |
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crypto_xor(dst, src, bsize); |
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iv = dst; |
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src += bsize; |
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dst += bsize; |
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} while ((nbytes -= bsize) >= bsize); |
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memcpy(walk->iv, iv, bsize); |
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return nbytes; |
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} |
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static int crypto_cfb_encrypt_inplace(struct skcipher_walk *walk, |
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struct crypto_skcipher *tfm) |
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{ |
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const unsigned int bsize = crypto_cfb_bsize(tfm); |
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unsigned int nbytes = walk->nbytes; |
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u8 *src = walk->src.virt.addr; |
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u8 *iv = walk->iv; |
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u8 tmp[MAX_CIPHER_BLOCKSIZE]; |
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do { |
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crypto_cfb_encrypt_one(tfm, iv, tmp); |
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crypto_xor(src, tmp, bsize); |
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iv = src; |
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src += bsize; |
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} while ((nbytes -= bsize) >= bsize); |
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memcpy(walk->iv, iv, bsize); |
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return nbytes; |
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} |
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static int crypto_cfb_encrypt(struct skcipher_request *req) |
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{ |
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struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req); |
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struct skcipher_walk walk; |
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unsigned int bsize = crypto_cfb_bsize(tfm); |
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int err; |
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err = skcipher_walk_virt(&walk, req, false); |
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while (walk.nbytes >= bsize) { |
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if (walk.src.virt.addr == walk.dst.virt.addr) |
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err = crypto_cfb_encrypt_inplace(&walk, tfm); |
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else |
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err = crypto_cfb_encrypt_segment(&walk, tfm); |
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err = skcipher_walk_done(&walk, err); |
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} |
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if (walk.nbytes) { |
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crypto_cfb_final(&walk, tfm); |
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err = skcipher_walk_done(&walk, 0); |
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} |
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return err; |
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} |
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static int crypto_cfb_decrypt_segment(struct skcipher_walk *walk, |
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struct crypto_skcipher *tfm) |
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{ |
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const unsigned int bsize = crypto_cfb_bsize(tfm); |
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unsigned int nbytes = walk->nbytes; |
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u8 *src = walk->src.virt.addr; |
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u8 *dst = walk->dst.virt.addr; |
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u8 *iv = walk->iv; |
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do { |
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crypto_cfb_encrypt_one(tfm, iv, dst); |
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crypto_xor(dst, src, bsize); |
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iv = src; |
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src += bsize; |
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dst += bsize; |
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} while ((nbytes -= bsize) >= bsize); |
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memcpy(walk->iv, iv, bsize); |
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return nbytes; |
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} |
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static int crypto_cfb_decrypt_inplace(struct skcipher_walk *walk, |
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struct crypto_skcipher *tfm) |
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{ |
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const unsigned int bsize = crypto_cfb_bsize(tfm); |
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unsigned int nbytes = walk->nbytes; |
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u8 *src = walk->src.virt.addr; |
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u8 * const iv = walk->iv; |
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u8 tmp[MAX_CIPHER_BLOCKSIZE]; |
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do { |
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crypto_cfb_encrypt_one(tfm, iv, tmp); |
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memcpy(iv, src, bsize); |
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crypto_xor(src, tmp, bsize); |
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src += bsize; |
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} while ((nbytes -= bsize) >= bsize); |
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return nbytes; |
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} |
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static int crypto_cfb_decrypt_blocks(struct skcipher_walk *walk, |
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struct crypto_skcipher *tfm) |
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{ |
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if (walk->src.virt.addr == walk->dst.virt.addr) |
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return crypto_cfb_decrypt_inplace(walk, tfm); |
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else |
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return crypto_cfb_decrypt_segment(walk, tfm); |
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} |
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static int crypto_cfb_decrypt(struct skcipher_request *req) |
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{ |
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struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req); |
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struct skcipher_walk walk; |
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const unsigned int bsize = crypto_cfb_bsize(tfm); |
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int err; |
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err = skcipher_walk_virt(&walk, req, false); |
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while (walk.nbytes >= bsize) { |
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err = crypto_cfb_decrypt_blocks(&walk, tfm); |
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err = skcipher_walk_done(&walk, err); |
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} |
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if (walk.nbytes) { |
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crypto_cfb_final(&walk, tfm); |
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err = skcipher_walk_done(&walk, 0); |
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} |
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return err; |
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} |
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static int crypto_cfb_create(struct crypto_template *tmpl, struct rtattr **tb) |
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{ |
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struct skcipher_instance *inst; |
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struct crypto_alg *alg; |
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int err; |
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inst = skcipher_alloc_instance_simple(tmpl, tb); |
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if (IS_ERR(inst)) |
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return PTR_ERR(inst); |
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alg = skcipher_ialg_simple(inst); |
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/* CFB mode is a stream cipher. */ |
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inst->alg.base.cra_blocksize = 1; |
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/* |
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* To simplify the implementation, configure the skcipher walk to only |
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* give a partial block at the very end, never earlier. |
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*/ |
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inst->alg.chunksize = alg->cra_blocksize; |
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inst->alg.encrypt = crypto_cfb_encrypt; |
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inst->alg.decrypt = crypto_cfb_decrypt; |
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err = skcipher_register_instance(tmpl, inst); |
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if (err) |
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inst->free(inst); |
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return err; |
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} |
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static struct crypto_template crypto_cfb_tmpl = { |
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.name = "cfb", |
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.create = crypto_cfb_create, |
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.module = THIS_MODULE, |
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}; |
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static int __init crypto_cfb_module_init(void) |
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{ |
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return crypto_register_template(&crypto_cfb_tmpl); |
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} |
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static void __exit crypto_cfb_module_exit(void) |
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{ |
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crypto_unregister_template(&crypto_cfb_tmpl); |
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} |
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subsys_initcall(crypto_cfb_module_init); |
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module_exit(crypto_cfb_module_exit); |
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MODULE_LICENSE("GPL"); |
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MODULE_DESCRIPTION("CFB block cipher mode of operation"); |
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MODULE_ALIAS_CRYPTO("cfb"); |
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MODULE_IMPORT_NS(CRYPTO_INTERNAL);
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